Solid waste disposal can generally be defined as the disposal of normally solid or semi-solid materials, resulting from human and animal activities, which are useless, unwanted, or hazardous. Solid waste generally comprises: garbage, including decomposable wastes from food; rubbish, including combustible decomposable wastes, such as paper, wood, and cloth, or non-combustible decomposable wastes, such as metal, glass, and ceramics; ashes, including the residue of the combustion of solid fuels; large wastes, including demolition and construction debris and trees; dead animals; sewage treatment solids, including the material retained on sewage-treatment screens, settled solids, and biomass sludge; industrial wastes, including chemicals, paints, and sand; mining wastes, including slag heaps and coal refuse piles; and agricultural wastes, including farm animal manure and crop residues.
Today, the most common method of disposing of solid wastes in the United States is the deposition of such wastes on land or in landfills, which may account for more than ninety percent of the nation's municipal refuse. Incineration accounts for most of the remainder, while recycling and composting of solid wastes accounts for only an insignificant amount.
In modern landfills, refuse is spread in thin layers, each of which is compacted by heavy industrial equipment, such as bulldozers, before the next layer is spread. When about three meters of refuse has been laid down, it is covered by a thin layer of clean earth, which is also compacted. Notwithstanding their widespread use, there are a variety of problems associated with landfills. For example, suitable land must be within economic range of the source of the wastes because, typically, collection and transportation costs account for seventy-five percent of the total cost of solid waste management. Additionally, although pollution of surface and groundwater is believed to be minimized by taking such precautions as: lining and contouring the fill; compacting and planting the cover; selecting proper soil; diverting upland drainage; and placing wastes in sites not subject to flooding or high groundwater levels, such pollution remains a concern. Furthermore, gases are generated in landfills through anaerobic decomposition of organic solid waste. If a significant amount of methane gas is present, it may be explosive; therefore, proper venting and burning of the methane gases are often necessary to eliminate or alleviate these dangerous conditions.
As mentioned, incineration is another solid waste disposal method in use today. Incinerators of conventional design burn waste on moving grates in refractory-lined chambers. The combustible gases and the solids they carry are burned in secondary chambers. In addition to heat, the products of incineration include the normal primary products of combustion, including carbon dioxide and water, as well as oxides of sulfur and nitrogen, gaseous pollutants, and nongaseous products such as fly ash and unburned solid residue. The incineration process is far from ideal, introducing harmful by-products and pollutants into the atmosphere. Additionally, incineration methods are known to destroy the useful hemicellulose component of woody cellulose materials contained in solid waste.
Because landfill and incineration methods of disposal are known to pose significant environmental problems and concerns for municipalities, government, private industry, and individuals, recycling has become an attractive alternative to these methods. The treatment and handling of solid waste for reuse is particularly attractive. Such treatment and handling of solid waste is referred to herein as resource recovery.
A traditional hydrolyzer is typically used for processing organic material, for example, animal carcasses or parts thereof, including organic wastes generated during meat and poultry production for human consumption. Traditional hydrolyzer apparatuses have various shortcomings. For example, some traditional hydrolyzers are designed to treat only a single batch of organic waste at a time. More specifically, a traditional batch hydrolyzer must be loaded with a batch while at an ambient pressure and temperature. It is then sealed, brought up to and held at an elevated pressure and temperature until the batch has been processed. Next, it is brought back down to ambient pressure and temperature, unsealed, and the processed batch of is removed. Such hydrolyzers can also become clogged while the batch is being processed, creating additional problems. Specifically, pressure and heat are slowly transferred to the batch after it is placed in the traditional batch hydrolyzer, creating a tendency for the organic waste to congeal and develop a clumpy or gummy consistency. Waste having a clumpy or gummy consistency requires a greater amount of time to process. Although certain mixing mechanisms provided within the traditional hydrolyzer can reduce this problem, there remains a risk of repeated and continuous clogging. At times, such clogging must be remedied by bringing the pressure and temperature down to ambient, unsealing the hydrolyzer, manually unclogging the hydrolyzer, resealing the hydrolyzer, bringing the hydrolyzer back to elevated pressure and temperature, and allowing the processing of the batch to continue.
Other traditional hydrolyzers are designed to handle a low-level flow of organic waste rather than merely a single batch at a time; however, these traditional flow hydrolyzers are also rife with problems. A traditional flow hydrolyzer is an open system in which organic waste travels from an inlet, through a vessel having somewhat of an elevated pressure and temperature, and to an outlet. In an attempt to retain pressure and temperature within the vessel, the inlet and outlet openings are relatively small, limiting the amount of organic waste that can be transferred into and out of the hydrolyzer. Additionally, because the system is open, it is difficult to reach pressures above about 50 psi, which results in slower processing. Indeed, because the system is open, pressure and heat must be continuously pumped into the vessel to even maintain pressures of about 50 psi. The open system also creates a risk of a forceful or violent ejection of material from the area of elevated pressure through the inlet or outlet.
Additionally, because material must flow through such traditional hydrolyzers, they must be equipped with a system for shuttling material through the vessel from the inlet to the outlet. Such systems may include a rotating spindle with attached paddles for pushing the material through the vessel. However, as with the batch hydrolyzers, there is a certain tendency for the organic waste to congeal as it enters the vessel, and it may clump around the paddles, clogging the vessel. The above-mentioned problems are just of few of those making treatment of waste using either a traditional batch hydrolyzer or a traditional flow hydrolyzer inefficient and time intensive.
Existing waste disposal systems have a variety of problems. Chief among them is that the use of landfills and incinerators ignore the useful components of solid waste and pose significant environmental problems. Also, existing apparatuses for the recovery of subsets of solid waste, such as organic wastes, are inefficient in that they must be shut down for significant periods of time when becoming clogged with debris.
Accordingly, there remains a need in the art for apparatuses and methods of resource recovery which do not pose environmental problems and are efficient.